feat: implement location events & error handling (Step 10.2)

- Add LocationService with create/rename/archive methods
- Add LocationProjection for event handling
- Add admin-only location management routes at /locations
- Add error response helpers (error_response, error_toast, success_toast)
- Add toast handler JS to base template for HX-Trigger notifications
- Update seeds.py to emit LocationCreated events per spec §23
- Archived locations block animal moves with 422 error

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tests/test_service_animal.py

@@ -240,6 +240,9 @@ class TestAnimalServiceTransactionIntegrity:
 
     def test_no_partial_data_on_projection_error(self, seeded_db, event_store, valid_location_id):
         """If projection fails, event is not persisted."""
+        # Count events before the test (seeds create LocationCreated events)
+        event_count_before = seeded_db.execute("SELECT COUNT(*) FROM events").fetchone()[0]
+
         # Create a registry with a failing projection
         from animaltrack.projections import Projection, ProjectionError
 
@@ -264,9 +267,9 @@ class TestAnimalServiceTransactionIntegrity:
         with pytest.raises(ProjectionError):
             service.create_cohort(payload, ts_utc, "test_user")
 
-        # Verify nothing was persisted
-        event_count = seeded_db.execute("SELECT COUNT(*) FROM events").fetchone()[0]
-        assert event_count == 0
+        # Verify no new events were persisted (count unchanged from before)
+        event_count_after = seeded_db.execute("SELECT COUNT(*) FROM events").fetchone()[0]
+        assert event_count_after == event_count_before
 
         animal_count = seeded_db.execute("SELECT COUNT(*) FROM animal_registry").fetchone()[0]
         assert animal_count == 0